Nano-Optics and Plasmonics

Control light at the nanoscale

Controlling light at the nanoscale, at length scales far below the diffraction limit of far-field optics, has great promise for applications ranging from heat-assisted magnetic recording and efficient light capture for solar energy to highly sensitive chemical and bio-sensors. Key to nanoscale light control are surface plasmon polaritons, infrared or visible-frequency waves at a metal-dielectric or metal-air interface, involving both charge motion in metal and electromagnetic waves in air, or dielectric. While use of plasmonic effects in art goes back more than 1,000 years (the Lycurgus cup, for example), and its scientific investigation goes back at least 100 years (Gustav Mie), recent decades have witnessed a surging scientific interest in both the investigation of plasmonics and their use as a scientific tool. Aside from metal nanoparticles, other instances of plasmon polaritons notably include graphene and analogous phonon polaritons, which also have been observed in the related boron nitride (see X.G. Xu, B.G. Ghamsari, J-H. Jiang, L. Gilburd, G.O. Andreev, C. Zhi, Y. Bando, D. Golberg, P. Berini, and G.C. Walker, "One-Dimensional Surface Phonon Polaritons in Boron Nitride Nanotubes," Nature Communications 5 (2014): 4782, doi:10.1038/ncomms5782).

The direct optical technique of scanning probe infrared imaging implemented on the Inspire is intrinsically and uniquely suited to investigating optical fields at the nanoscale, such as on plasmonic structures. The technique itself is an example of nano-optics, using nanoscale light confinement in the optical near field of a sharp metallic (“optical antenna”) structure as its means of interrogation. Thus, coupling to and probing plasmonic properties, for example mapping out plasmon polaritons and measuring their wavelength on graphene, is a natural and powerful application for Inspire.